The invention relates to specific amphiphilic copolymers containing silane units, a film comprising at least one monomolecular layer of these molecules on a solid support (=so-called layer elements), and a process for the preparation of the layer elements and their use.
Ordered layers of organic polymers having long-chain side groups are predominantly prepared by using the Langmuir-Blodgett (LB) method. In this method, molecules are spread on a water surface and the long alkyl side groups are aligned in parallel by decreasing the area per molecule. At a constant pressure, the molecules are applied to a substrate by immersion and withdrawal. Per dipping operation, one monomolecular layer is transferred with retention of its order.
LB films are constructed by using amphiphilic molecules, i.e. molecules having a hydrophilic end (a "head") and a hydrophobic end (a "tail"). In order to achieve higher stability of the LB films, polymeric LB films have also already been prepared.
Preparation of polymeric LB films can be carried out by polymerization of unsaturated amphiphiles after formation of the monomer film. However, organic polymers having long alkyl side chains have also already been used directly for preparation of the layer (WO 83/03165, R. Elbert, A. Laschewsky and H. Ringsdorf, J. Am. Chem. Soc. 107, 4134-4141 (1985)). Copolymer films have also already been described (A. Laschewsky, H. Ringsdorf, G. Schmidt and J. Schneider, J. Am. Chem. Soc. 109, 788-796 (1987)). In these copolymers, one of the comonomers carries at least one long alkyl chain, while the second monomer is water-soluble, or carries at least polar and hydrophilic groups. If such polymer films are intended to be used as resist materials, such as, for example, described by R. Jones, C. S. Winter, R. H. Tredgold, P. Hodge and A. Hoorfar, Polymer 28, 1619-1626 (1987), the problem of insufficient etching stability of these films during plasma etching arises.
However, it is known from resist technology that the etching stability of photoresists in an oxygen plasma can be drastically increased by incorporating silicon compounds. Thus, aliphatic and/or aromatic hydroxyl-carrying polymeric binders have been described which contain silanyl groups in the side chain which, as components of a photosensitive mixture, give this mixture increased resistance to plasma etching (EP-A-0,337,188). The photosensitive layer, which is formed by spin-coating the substrate with a resist solution containing such a binder and compounds from the class of compounds of o-quinone diazides, has a layer thickness of 0.3 to 10 .mu.m. A disadvantage for microelectronic applications, for example high-resolution electron beam lithography, is the relatively high layer thickness of resist films of this type.
Furthermore, Langmuir-Blodgett layers of amphiphilic polysiloxanes are known (Adv. Mater. 3 (1991), 27). It is true that they have good etching resistance in an oxygen plasma, but for many applications they have only insufficient temperature resistance, owing to the siloxane main chain.
Accordingly, the object is to prepare polymers from which Langmuir-Blodgett films can be formed which have improved resistance to temperature and plasma etching.